Sounds like an air leak or a blocked filter. Thoroughly check fuel hose and fittings for leaks including all under cowling fittings. Pump bulb with cowling on, wait 5 minutes, then take cowling off. If it smells like gas, find out where it is coming from.
I think those have a combination separator/filter under the cowling, if yes I would replace it unless it has been done very recently. Do test run and see if performance improves.
Grouse